Our overall objectives are to obtain vital information for effective treatment and prevention of thromboembolic diseases. Our working hypothesis for achieving the above objectives are as follows: 1) Hypercoagulability is a condition in which coagulation tendency of blood is increased by tissue thromboplastin released into the circulation from injured vessels. 2) This form of hypercoagulability precedes the onset of thrombosis. 3) Therefore, the diagnosis of hypercoagulability might be a good way for prevention of thrombosis. 4) We have shown that vascular injury releases vascular plasminogen activators into circulation which secondarily generate plasmin from plasminogen. 5) Therefore, the detection of plasmin generation might be a good criterion for the diagnosis of vascular injury and consequently hypercoagulability. At present we are studying in vivo behavior of I- 125-plasmin in dogs and also trying to define ideal conditions for plasmin generation.